This application is based upon and claims the benefit of priority from the corresponding Japanese Patent Application No. 2010-245808 filed on Nov. 2, 2010, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a recording medium storage cassette for storing a recording medium of a sheet form, which is to be used in an image forming apparatus such as a digital copying machine and a laser printer, and to an image forming apparatus including the recording medium storage cassette.
2. Description of Related Art
Conventionally, there has been widely used a sheet feeding cassette for storing a plurality of stacked sheets (recording media) and for conveying the sheets one by one in a separated manner to an image forming portion of an image forming apparatus main body in accordance with an image forming operation.
A configuration of a conventional sheet feeding cassette is described. FIG. 5 is a cross-sectional side view of a conventional sheet feeding cassette 10. A bundle of sheets 26 set in a cassette base 25 of the sheet feeding cassette 10 are pressed against a pickup roller 29, which is provided on an apparatus main body side, at a predetermined pressure, owing to the elevation of a sheet stacking plate 28 which is vertically raised and lowered by a lifting mechanism (not shown). Here, when a printing operation of the image forming apparatus is started, the pickup roller 29 and a feeding roller 30a of a feeding roller pair 30 are driven and rotated in directions indicated by the arrows of FIG. 5.
Generally, several sheets 26 on the upper side of the bundle set on the sheet stacking plate 28 are fed to the feeding roller pair 30 by the pickup roller 29. The feeding roller pair 30 includes the feeding roller 30a and a separation roller 30b which is provided in press-contact to or apart from the feeding roller 30a. The separation roller 30b has a torque limiter built therein, and is rotated with the feeding roller 30a in accordance with the rotation thereof only when the rotational load exceeds the predetermined torque. The separation roller 30b separates only the uppermost sheet of the several sheets fed to the feeding roller pair 30, to thereby convey the sheet toward a sheet conveyance path 11. The cassette base 25 is provided with a trailing end cursor 31 for aligning the trailing ends of the sheets 26, the trailing end cursor 31 being movable in a sheet conveyance direction (lateral direction in FIG. 5).
In the sheet feeding cassette 10 described above, there has been a problem that, when the bundle of the sheets 26 are set on the sheet stacking plate 28, or when the sheets 26 once set are removed and then the sheets 26 having different size or paper quality are reset, the workability is lowered because a wall portion provided upright at a peripheral end portion of the cassette base 25 disturbs the work.
In this context, there have been proposed various sheet feeding cassettes which enable smooth supplying and removing of the sheets with respect to the sheet feeding cassette. For example, there is known a configuration in which a notch portion is provided from the side surface to the bottom surface of the sheet feeding cassette so that at least a hand is insertable. Further, there is also known a configuration in which a sheet abutment portion (trailing end cursor), which is integrally formed with a cassette plate (sheet stacking plate), is notched in part so as to provide a finger inserting portion.
By the way, when the sheet is fed from the sheet feeding cassette as described above, there is a problem that a flapping noise of the sheet trailing end is generated. Specifically, when one sheet 26 is conveyed toward the sheet conveyance path 11, as illustrated in FIG. 6, after passing through a nip portion between the pickup roller 29 and the sheet stacking plate 28, a trailing end 26a of the sheet 26 being conveyed is hit to an upper end of a wall portion 25a positioned in a sheet feeding direction of the cassette base 25 by the restoring force of the sheet 26. Thus, a sheet conveyance noise (flapping noise) is generated.
This flapping noise is a so-called impulse response, which corresponds to a momentarily generated high-pitched sound, and hence is extremely annoying for a user. In recent years, there has been an increasing demand for noise-reduction, and therefore a measure against the flapping noise of the sheet trailing end, which is one of the factors of noise, has become important. However, with the above-mentioned method of providing the notch portion in the side surface of the sheet feeding cassette or a part of the trailing end cursor, it has been incapable of reducing the flapping noise of the sheet trailing end.
As a conventional measure, a member having cushioning properties such as an elastic body is fixed to a place to which the sheet trailing end is hit, to thereby reduce the flapping noise. However, because of the addition of the member, this method causes increase in material cost and manufacturing cost, and further, there is a fear that the fixed member causes harmful effects such as a jam of the sheet.
As a method of reducing the flapping noise of the sheet trailing end, for example, there is known a sheet feeding apparatus in which a plurality of ribs are formed on a guide surface of a turn guide which reverses the sheet fed from the sheet cassette and guides the reversed sheet to an image transfer portion, and a projected portion of the rib, which is projected toward the leading end of the sheet cassette, is shaped so as to become lower toward both ends from a center of the turn guide.
However, the above-mentioned technology is a technology for preventing generation of the flapping noise caused by the collision of the turn guide and the trailing end of the sheet fed from the sheet cassette, and is not a technology for preventing the flapping noise caused by the collision of the sheet trailing end and the wall portion of the sheet cassette. Further, although the sheet is conveyed in the sheet feeding direction while the center portion in the width direction thereof, which is nipped between the feeding roller pair, bends downwardly, in the above-mentioned sheet feeding apparatus, the rib at the center of the turn guide has the largest height. Thus, there has not been disclosed any technological idea for avoiding the collision of the sheet and the rib in consideration of the sheet bending.